Add a doctest for previously suggested fix

Author: furthermares

Diff for: data_structures/trie/radix_tree.py

@@ -43,6 +43,11 @@ def insert_many(self, words: list[str]) -> None:
             words (list[str]): list of words
 
         >>> RadixNode("myprefix").insert_many(["mystring", "hello"])
+
+        >>> root = RadixNode()
+        >>> root.insert_many(['A', 'AA'])
+        >>> root.nodes['A'].nodes['A'].prefix
+        'A'
         """
         for word in words:
             self.insert(word)